1. Field of the Invention
The present invention relates to a portable navigation system, and more particularly, to a portable vehicle navigation system carried in or removably mounted to a vehicle.
2. Description of the Related Art
One type of conventional vehicle navigation apparatus is mounted on a vehicle and is generally self-contained, except for receiving inputs on vehicle location from a source external to the navigation apparatus. This navigation apparatus typically includes a mass memory storage device, such as a CD-ROM (or equivalent) in which pre-determined map data is stored, a display unit for displaying map information (including the starting, current and ending positions of the vehicle and the route between starting and ending positions), a vehicle position sensing unit such as a GPS receiver for detecting the present position and present direction of a vehicle, and a controller for receiving input from the vehicle position sensing unit and the mass memory storage device and calculating the optimal route to the ending position from the starting position and from the present position.
In operation, the apparatus reads out map data containing the present position of the vehicle from the mass memory storage device, draws a map image including the vehicle position at the center thereof based on the map data, displays the map image on a display screen, and fixes a vehicle position mark (location cursor) at the center of the display screen. This indicates where the vehicle is located at present to the driver, at a glance, by scrolling map images on the screen depending upon the movement of the vehicle, or by moving the vehicle position mark while fixing the map image on the screen. Maps stored in mass memory storage device are divided into longitudes and latitudes each having a suitable width in accordance with a scale (e.g. 1/12,500, 1/25,000, 1/50,000, 1/100,000); roads are displayed by a set of coordinates of nodes represented by the longitudes and latitudes. A road is composed of two or more nodes connected to each other, and a road portion connecting two nodes is called a link. The map data is composed of (1) a road list, a node table, a node list constituting crossings, a map matching consisting of a crossing network list, and a route searching road layer; (2) a background layer for displaying roads, buildings, facilities, parks, rivers and the like on a map screen; and (3) a character/symbol layer for displaying the characters, map symbols and names of administrative districts such as names of cities, towns and villages, names of roads, names of crossings (road junctions) and names of buildings. The navigation apparatus is provided with a route guiding function, thereby allowing the driver to easily travel toward a desired destination without losing his way. The route guiding function automatically searches for a nearest route connecting a starting location to a destination by carrying out a simulation using map data, and stores the result of the simulation as guided route data, wherein the driver can simply understand an optimum route to his destination as follows.
Another type of conventional vehicle navigation apparatus is similar to the first type, except it but relies on access to external sources to receive updates of maps and/or for calculations of optimal routes. This navigation apparatus typically includes a wireless communication device, such as a cellular or PCS telephone, for downloading map data from an external source of map data and communicating with an external computing system for determining optimal route from desired starting and destination locations, a memory storage device, such as RAM (or equivalent) in which is stored map data downloaded from the external source, a display unit for displaying map information (including the starting, current and ending positions of the vehicle and the route between starting and ending positions) and a vehicle position sensing unit such as a GPS receiver for detecting the present position and present direction of a vehicle. In operation, this apparatus functions substantially similar to the previously described self contained apparatus, except that the map data is downloaded from the external source and the route guiding function is performed by the external computing system.
Digital map distributions are targeted to a wide market and are concerned with the collection of data, not the use of it. They are distributed mostly in a text format—universal, but large—and most of the time contain many more data sets than the application requires. So a conversion process is always required to distill out the target data. This is illustrated by the fact that every database comes with a conversion utility. This process usually accounts for the largest unanticipated time requirement.
While the present navigation apparatuses are generally adequate, there is a need for a portable version of the same, so that one navigation apparatus can be readily used in more than one vehicle. There is also a need for a portable navigation apparatus that makes use of a mass storage device other than CD-ROMs or similar devices that contribute to relatively large form factors and relatively large power consumption. There is also a need for such a device having an improved map that more readily allows the position determined by the position-sensing device to be correlated with a position on the stored map. There is also a need for such a device having a means of conveying route information to a driver by voice rather than a display.